1. Field of the Invention
This invention relates to improvements in circuits for testing cardiac pacers, and, more particularly, to a circuit for testing the sensitivity of a cardiac pacer.
2. Description of the Prior Art
Variations in the sensitivity of a heart pacer, particularly heart pacers of the so-called demand and synchronous types, have been recognized. In general, prior concerns have been expressed in heart pacer sensitivity variations with variations in the supply voltage. For example, if the supply voltage to an implanted cardiac pacer becomes too low to enable the pacer to properly sense R-waves, or other heart produced waveforms, to produce the desired result (i.e. inhibiting the pacer, synchronizing subsequent pulses, etc.), the pacer may be ineffective for its intended purpose.
Thus, pacers have been proposed which include means for varying the sensitivity of the pacer in known amounts for the purpose of determining the "capture margin" to produce an indication of the remaining pacer battery lifetime. This is done, for instance, in U.S. Pat. Nos. 3,837,348, and 3,857,085.
Insofar as is known to applicant, however, there is no apparatus which is suitable for directly measuring the sensitivity of the pacer to a particular voltage waveform. It is desirable, for example, to measure the sensitivity of a pacer under consideration to a waveform which varies with time as a function of the sine.sup.2 of a 25 hertz signal.